Is my brother considered an infidel for not pronouncing the word "mustateera" correctly in a verse from Surat Al-Insan, and am I considered an infidel for not declaring him an infidel?

The questioner is suffering from obsessive thoughts related to disbelief (kufr) and mockery. She must discard these thoughts and not dwell on them, as dwelling on obsessive thoughts leads to doubt, confusion, and religious distress.

Her brother's pronunciation of the letter "Rāʾ" does not indicate any mockery. The emphatic pronunciation of "Rāʾ" (tafkhīm) is consistent with the recitation of the majority of reciters (qurrāʾ), and the default for "Rāʾ" is tafkhīm, except in specific cases according to Warsh from the path of Al-Azraq.